This invention relates generally to formed wire box spring assemblies and more particularly to formed wire box spring assemblies which utilize shaped metal cross rails which locate and support the formed wire springs in the assembly.
U.S. Pat. No. 3,680,157 dated Aug. 1, 1972 and assigned to the assignee of this application discloses a box spring assembly of the type to which this invention relates. In the box spring assembly shown in U.S. Pat. No. 3,680,157, the formed wire springs are supported in aligned slots formed in the upright webs of the frame cross rails. Such slots are conventionally formed in a punch press wherein the punch is of a smaller size than the die for clearance purposes. This results in a slot edge surface having a burnished land area and a larger rough and pock marked fracture area. Only the land area can function effectively as a bearing surface for the spring torsion bars.
The present invention is an improvement over the box spring assembly shown in U.S. Pat. No. 3,680,157 in that it enables easier assembly of the formed wire springs and the metal cross rails and provides improved bearing surfaces in the cross rails for the torsion bars in the springs that engage the cross rails. In the cross rails of this invention, metal from the webs is extruded to form bearing sections at the ends of the punched slots which are smooth surfaces of increased thickness relative to the web thickness, in contrast to the punched slot construction wherein the bearing area that is achievable is substantially less than the web thickness.